Notice: Undefined index: #icon_position in bootstrap_button() error

This is already added to every element: https://git.drupalcode.org/project/bootstrap/-/blob/a0cca7d11cfd1b269e2a...

I'm still seeing this randomly after cache clear. PHP 7.2, Bootstrap 3.26 , Drupal 7.69

I also see this. Drupal core 7.69, Bootstrap 7.x-3.26. Patch fixes the issue.

As I stated in #4, this is already added to every element:

https://git.drupalcode.org/project/bootstrap/-/blob/a0cca7d11cfd1b269e2a...

If you're receiving this error, it's likely due to something not using render arrays properly. For example: calling theme functions manually or using #theme instead of using #type as buttons (in D7) are expected to be elements; not theme hooks (that's how core implemented them at the time).

If you get this error, it only means that it's an error with either your custom implementation or some other contrib module.

Please track down that code and fix/file an issue with it instead.

This is not a "bug" in this project, it is designed and implemented the correct way.

Thanks for your help @markcarver. Your reply lead me to the offending code in a custom module..

<?php
          'close' => array(
            '#theme' => 'button',
            '#value' => t('Close'),
            '#button_type' => 'button',
            '#attributes' => array(
              'class' => array('btn', 'btn-default'),
              'data-dismiss' => 'modal',
            ),
          ),
?>

I changed it to the below and no longer get the error.

<?php
          'close' => array(
            '#markup' => l('&times;', '', array(
              'attributes' => array(
                'class' => array('btn', 'btn-default'),
                'data-dismiss' => 'modal',
              ),
              'fragment' => 'close',
              'html' => TRUE,
            )),
          ),
?>

Changing '#theme' => 'button' to '#type' => 'button' should have also worked.